The present invention relates generally to an apparatus for slicing veneer, and, more particularly, to a vacuum holding device used to hold the material being sliced.
Veneer slicers are machines used for slicing thin wood veneer from pre-conditioned logs, commonly called "flitches". The logs are usually pre-conditioned by cutting them lengthwise in half and by soaking them in water. Presently, the flitch is conventionally held against a flat surface of the slicer by mechanical clamps, commonly called "dogs" and this entire assembly is moved in a vertically reciprocating motion. A sharp knife is then moved incrementally toward the flitch, eventually making contact to slice off thin sheets of veneer.
Using dogs to hold the flitch in place results in wasted material, since the thickness of the flitch between the flat holding surface and the top of the dog cannot be sliced by the knife. The remaining material, commonly called a "backing board" is often approximately 20 millimeters in thickness. It is readily apparent, then, that conventional dog clamping systems result in considerable waste of material.
Another problem caused by using dogs to hold the flitch in place is that the uneven pressure exerted by the dogs, coupled with the reduced strength of the flitch as material is cut away, can cause the flitch itself to bend or curl during the latter slicing stages. This results in an inferior product and wasted material.
The general concept of using a vacuum to hold the flitch in place is known, although not heretofore accomplished successfully in practice. U.S. Pat. No. 4,693,458 (Leweche et al.), for example, discloses a clamping arrangement for lumber elements, which elements are held in place by a vacuum. Upon information and belief, this device, used for sawing wood as opposed to slicing veneer, would not function satisfactorily in a veneer slicing operation (and may not function satisfactorily even in a typical wood sawing operation.) The reason is that, in veneer processing, the wood is preconditioned by soaking in water, which results in a large amount of wood debris and wood resin from the saturated flitch. This contaminate material is sucked up by the vacuum and quickly plugs up the orifices, valves, and pumps used in the system. The vacuum is eventually lost, and the flitch can no longer be held to the holding surface.
Thus, a longfelt need has existed for a vacuum holding device for a veneer slicer, which device is capable of sucking wood debris and resins without losing vacuum.